The disclosure relates generally to turbomachine blades, and more particularly, to a blade having one or more corrugated outer surfaces to accelerate a mixing process from the source of a wake to minimize inflated unsteady mixing that occurs within a downstream blade row.
Turbomachine blades include airfoils that accelerate flow through contraction of area and the introduction of tangential velocity. The relative flow velocity exiting, for example, a gas turbine airfoil is quite high, typically with Mach numbers of 0.5 or higher. The finite thickness of an airfoil trailing edge, however, creates a velocity deficit, i.e., a wake, which introduces losses in the flow through viscous mixing. FIG. 1 shows an example of a typical unsteady loss process for a turbine rotating blade row 10 operating behind a turbine stationary vane row 12. At location 14, a wake is generated by a finite trailing edge thickness of the airfoil of vane row 12, resulting in aerodynamic losses due to mixing of the wake with the mainstream. At location 16, the wake interacts with a potential field of a downstream rotating blade row 10, and it begins to distort. At location 18, the wake is segregated into discrete packages by the leading edge of airfoils in downstream rotation blade row 10. At location 20, a pressure gradient in the airfoil passage (between blades of blade row 10) causes wake packets to stretch and migrate, causing aerodynamic losses due to mixing of the wake packets (referred to as “free stream mixing”). That is, when the wake is ingested into a downstream stationary blade row 10, the wake undergoes a stretching and dilation process that magnifies the losses associated with the mixing. At location 22, the wake packets interact with the boundary layer of the blades in blade row 10 downstream of the airfoils' wake, causing further aerodynamic losses (referred to as “airfoil surface losses”). Unsteady loss caused by this phenomenon is present in all turbomachinery in various forms.
In order to address the above challenges, blades having airfoils with enhanced wake mixing structures have been proposed. The wave mixing structures can take a variety of forms such as crenulated or serrated trailing edges on the airfoils. These structures, however, have been limited to trailing edges of the airfoil.